Dynamic behavior of the liquid flow coalescing with a droplet in hydrophobic microchannels

In this study, the dynamic behavior of the moving liquid column coalescing with a sessile droplet in a hydrophobic microchannel under pressure driven flow conditions is numerically investigated using coupled Volume of Fluid with Level Set (CLSVOF) interface tracking method implemented in ANSYS-Fluent 14.5 in conjunction with the continuum surface force (CSF) model. Numerical result reveals that the coalescence between the moving liquid column and droplet can accelerate the original liquid column movement. Effects of the wettability, head pressure, and droplet size and position are also investigated. It is found that the velocity increment ratio increases with increasing the contact angle and decreasing the head pressure. Larger droplet and smaller distance between the droplet and inlet can result in a larger velocity increment ratio as a result of higher surface energy and lower viscous dissipation energy. The maximum velocity increment ratio of 0.17 is obtained with a 10000-µm3 droplet that is positioned at 200 µm in a microchannel with 100 µm in width and 300 µm in length and contact angle of 120°.